The story of the GUI-based computers at Apple is a bit more complicated than what most people have in mind, between the Lisa and Macintosh projects.
For instance, the Lisa is not as much a Steve Jobs project as many think. Even despite the name (which is thought to be his daughter's name, ironically). Sure he came back from Xerox with the ideas, but after that, things got awry.
He was actually set aside for its development, and embarked on the Macintosh project - that Apple didn't care much about at the time - as a kind of revenge, or second chance.
When Apple started to become big in the early 80's, Steve Jobs, despite being the cofounder, was not that well positioned at Apple. (And everyone knows he eventually got kicked out.)
It's a pretty interesting story, both for the technical and human aspects, so I recommend reading it as well!
As to Xerox, let's also recall that Niklaus Wirth himself spent a whole year at Xerox as a sabbatical, and also came back with ideas that would lead to the development of his workstations (like the Lilith).